In ordinary catalytic cracking processes, various metallic contaminants which are present in hydrocarbonaceous feedstock, particularly vanadium, nickel, copper and iron, cause the degradation and/or deactivation of the catalytic cracking catalyst. Particularly susceptible to vanadium contamination are crystalline aluminosilicate zeolites, either natural or synthetic. This deactivation causes distillate yield loss, particularly through loss of active acid cracking sites, as well as metal poisoning via secondary dehydrogenation and coking reactions caused by the deposition of these heavy metals on the catalyst. Remedial technology has evolved in various ways to deal with this metals contaminant problem.
For example, one method uses metallic compound additives to the catalyst or the hydrocarbon oil which compound additives serve to passivate the metallic contaminants on the catalyst. U.S. Pat. No. 4,432,890, Beck et al., teaches a catalyst composition comprising a crystalline aluminosilicate zeolite dispersed in an amorphous inert solid matrix containing a metal additive. The metal additive may be introduced into the catalyst during the cracking process or during catalyst manufacture. Metal additives include water soluble inorganic metal salt and hydrocarbon soluble inorganic metal salts, and hydrocarbon soluble organometallics of selected metals. U.S. Pat. No. 3,977,963, Readal et al., teaches a method of negating the effects of metals-poisoning on a cracking catalyst by contacting the metal-contaminated catalyst with a bismuth or manganese compound. U.S. Pat. No. 4,101,417, Mitchell et al., would add 2000 ppm of tin to the catalyst for the same purpose. In U.S. Pat. No. 4,784,752, Ramamoorthy et al., disclose the addition of a passivating agent containing bismuth in a weight ratio of bismuth to "nickel equivalents" consisting of nickel, iron and vanadium. In U.S. Pat. No. 4,083,807, Mitchell et al., an improved cracking catalyst is obtained by incorporating into a crystalline aluminosilicate catalyst by ion exchange a substantial concentration of a metal selected from antimony, bismuth and manganese. U.S. Pat. No. 4,990,240, Pasek et al., teaches zeolite passivation of vanadium in terms of a passivation factor greater than 2.0 for selected Group IIA metal compounds. U.S. Pat. No. 4,929,583, Pasek et al., claims the catalyst composition comprising this vanadium passivator. U.S. Pat. No. 4,036,740, Readal et al., teaches a selected catalytic cracking process using a bismuth, antimony or manganese treating agent to maintain a selected volume ratio of carbon dioxide to carbon monoxide in the gaseous effluent. The disclosures of the aforementioned patents are incorporated herein as if fully set forth in ipsis verbis.
Another mechanism includes the use of various diluents as metals passivators or traps. The traps contain materials which will chemically combine with and effectively tie up the offending materials. These traps have proved particularly effective with regard to vanadium.
One strategy utilizing this mechanism involves the use of dual particle systems wherein the cracking catalyst, usually zeolitic, is contained on one particle or component of the system, and a diluent or vanadium trap is contained as a separate, distinct entity on a second particle or component of the system. U.S. Pat. No. 4,465,588, Occelli et al., discloses a process for cracking high metals content feedstock using a novel catalyst cracking composition comprising a solid cracking catalyst and a separate and distinct diluent which contains materials selected from magnesium compounds, or a selected magnesium compound in combination with one or more heat-stable metal compounds. Among the magnesium-containing compounds specified is magnesium clay sepiolite. U.S. Pat. No. 4,465,779 teaches the cracking catalyst of '558 itself. U.S. Pat. No. 4,615,996, Occelli, teaches a dual-function cracking catalyst composition comprising a solid cracking catalyst and a separate, distinct particle diluent containing substantially catalytically inactive crystalline aluminosilicate. U.S. Pat. No. 4,466,884, Occelli et al., teaches a process wherein the separate and distinct entity diluent contains antimony and/or tin, supported on an inert base selected from the group consisting of magnesium-containing clay minerals, including sepiolite. U.S. Pat. No. 4,650,564, Occelli et al., also teaches a process for cracking high metals content feedstock comprising contacting the feed with a dual particle catalyst cracking composition comprising a solid cracking catalyst and, as a separate and distinct entity, an alumina diluent. U.S. Pat. No. 4,944,865, Occelli et al., also teaches a dual particle catalytic cracking system comprising a cracking catalyst and a second component comprising magnesium oxide. U.S. Pat. No. 4,707,461, Mitchell et al., discloses a catalyst composition comprising zeolite, matrix, and a calcium-containing additive comprising substantially amorphous calcium silicate as a separate and discrete component. A preferred calcium additive component comprises dolomite.
One primary issue involving the use of the dual particle systems in fluid catalytic cracking is that the effect of the diluent particle on yield is such that the activity of the active catalyst must be very high in order to compensate for the dilution effect. It would therefore be helpful to develop a dual particle catalyst wherein the diluent could be added in low amounts and have enhanced metals scavenging ability, in particular vanadium. Secondarily, it would be advantageous for the catalyst system to demonstrate higher sulfur tolerance than previous known systems, as some feeds requiring processing have high enough sulfur levels to cause process difficulties with known catalysts.
Related patent U.S. Pat. No. 4,988,654, Kennedy and Jossens, claims such a dual component catalyst composition for the catalytic cracking of metal-containing hydrocarbonaceous feedstock comprising as a first component an active cracking catalyst; and as second component, a separate and distinct particle comprising a selected calcium and magnesium containing material; a magnesium containing material comprising a hydrous magnesium silicate; and a selected binder. U.S. Pat. No. 5,002,653, Kennedy and Jossens, claims the catalytic cracking process with the dual component catalyst of '654. Related patent application U.S. Ser. No. 590,538, filed Sep. 27, 1990, claims the second component of the dual component catalyst system. The disclosure of U.S. Ser. No. 590,538 is incorporated herein by reference. The preferred second component comprises dolomite and sepiolite. U.S. Pat. No. 4,196,102, Inooka et al., relates to a hydrotreating catalyst comprising selected catalytic metals on a sepiolite carrier. U.S. Pat. No. 4,343,723, Rogers et al., teaches the use of clays with crystalline aluminosilicate zeolite in catalytic compositions. U.S. Pat. No. 4,439,312, Asaoko et al., provides a catalyst for hydrotreating heavy oil, including a carrier which is a calcined mixture of selected magnesium silicate and selected pseudoboehmite. U.S. Pat. No. 4,929,338, Wormsbecker, reports a catalytic cracking catalyst for vanadium-containing hydrocarbons having a selected dolomite component mixed with a zeolite cracking catalyst as an integral component or as a separate additive. The disclosure of the aforementioned patents are incorporated herein as if fully set forth in ipsis verbis.
To carry this strategy one step further, it would be advantageous if, for example, a dolomite/sepiolite particle additive when added to an FCC catalyst inventory contaminated with vanadium, either in situ, in the FCC unit, or by treatment of the contaminated catalyst ex situ, would take up vanadium from the catalyst. It would also be advantageous if a metallic passivator, as heretofore described, were incorporated into the additive to render nickel contaminants inert in place on the catalyst. It would be especially advantageous if after such treatment with the additive, the catalyst would regain its activity without removal of the additive from the catalyst inventory. However, it would suffice if re-activated catalyst were separable from the additive, separated and reused.
This strategy, if successful, would result in a rejuvenated catalyst having the following benefits: Revived catalyst activity offering higher FCC conversion or feed throughput; Removal of pore blocking vanadium; Reduced fresh catalyst consumption; The opportunity for accommodating heavier oil feedstocks, or residuum.